POTENTIAL-ENERGY SURFACES FOR THE LOW-LYING (2)A'' AND (2)A' STATES OF HO2 - USE OF THE DIATOMICS IN MOLECULES MODEL TO FIT AB-INITIO DATA

A DIM (diatomics in molecules) model utilizing a large basis set (34 2A″ and 32 2A′ states) was used to obtain the potential energy surfaces relevant to the chemical reaction H+O 2→OH+O. The ground state, 12A″, surface was fitted to 910 accurate ab initio points of Walch et al. [J. Chem. Phys. 94, 7068 (1991)]. The resulting fit accurately describes the C2v conical intersection in the regions for which ab initio data are available, and the linear conical intersection is accurately described in the H+O2 region. It is also an accurate global fit with an rms deviation of 0.096 eV (2.22 kcal/mol). The behavior of the low-lying excited states, 1 2A′, 22A″, and 22A′, appears to be qualitatively correct everywhere and quantitative near the low-lying conical intersections. The DIM formulation allows the computation of the gauge potential relevant for the description of the geometric phase and non-adiabatic effects in multi-surface reactive scattering calculations. © 1995 American Institute of Physics.